Most listings are in the $20's per square foot per year. The Manassas County submarket is going through a decrease in rates. In the last 3 months, the median rate decreased $5 per sqft per year. That's a 20% decrease in rent.
In the last 90 days, 30 listings have been listed, which means spaces most likley are going fast. You'll want to be prepared to make an offer immediately. About 7% of the available space in the Manassas County are subleases, so you will probably need to consider the implications of signing a direct lease with the building. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,490 sqft. Most buildings in this area are around 2 stories. Most buildings in this area were built in 1989 and are Class B.